The invention is directed to an installation for the control of a traffic light system by vehicles which are provided with devices for automatic determination of position or bearing.
It is obvious that with the constant increase in motorized transportation, and thus the increase of inner city traffic, public vehicles of local transit systems, such as buses and street cars, must provide their services in congested areas under constantly increasingly difficult conditions. However, it is precisely these forms of transportion that should be attractive to the user and efficient in their operation. This, in turn, involves the requirements of high speed, dense car succession and maintenance of schedules. An effective disposition of public local transportation facilities, therefore, dictates the possibility for enforced control of the green phases of traffic signals. Such an enforced control, however, is even more urgent in connection with the operation of emergency and police vehicles.
In street cars, such a request for the green phase can be triggered by means of track or trolley contacts. Where buses are involved, inductive loops usually are employed a few hundred meters ahead of the intersection. Either the presence only of a bus is determined by means of a loop, or the length of a bus may be measured by means of two loops. However, either arrangement can lead to erroneous report, for example, where trucks of a similar size are involved. While this disadvantage can be avoided by the utilization of a transmitter on the bus, there still remains the rather expensive installation of a recording cable from the loop to the traffic light.
In other systems, this disadvantage is avoided in that the request is emitted directly from the vehicle to a traffic light receiver over the atmosphere, for example, by means of radio, ultrasonics, or infrared radiation.